# DC current measure using Arduino nano

I have 75mV(50A & 100A) shunt and arduino nano, i want to measure current.

it is possible ?

At what voltage?

Ciao, Ale.

Sure, you use the Arduino to measure the voltage developed across the shunt as current flows.
value = analogRead( ); returns a number, 0 to 1023.
Take value and multiply be Vcc/1024.0 and there's your voltage.
float result = value * 5/1024.0;

0 to 40V DC and 0 to 100V DC

ok,

i don't know coding, please explain me.

I provided a code example. You need to spend some time in the Learning section to understand coding basics.

RajuR:
ok,

i don't know coding, please explain me.

Your shunt creates a voltage that is directly proportional to the current flowing through it.

From the specification 75mV/50A you have a ratio. so for each millivolt you measure, it represents 50/0.075 amps or 0.667 Amps per millivolt.

If you connect one side of the shut to GND and A0 to the Other end of the Shunt, and then use this end of the Shunt as your measured circuit ground. All of the power flowing through your measured circuit will produce a voltage that A0 will measure.

``````pinMode(A0,INPUT);
float voltage = rawValue; // convert integer value to Float
voltage = voltage * 5.0/1024.0; // Scale the Raw value to voltage.
float current = (50.0 / 0.075 )*voltage; // convert voltage to current using specification of Shunt

Serial.print(current,4); // print current with 4 decimal points
Serial.println(" Amps");
``````

Chuck.

I have 75mV(50A & 100A) shunt

Serial.print(current,4); // print current with 4 decimal points

Lol.

Wawa:
I have 75mV(50A & 100A) shunt

Serial.print(current,4); // print current with 4 decimal points

Lol.

What, don't you think 0.6667A per millivolt is enough resolution? I Assumed that he was measuring 50A.

:o

I admit that the Nano will be luck to measure 5mV. so, 3.2A will be his minimum Value >:(

Doesn't adding digits past the decimal point show Increased resolution?

Chuck.

P.S. I never said the printed values would have meaning, Just that they would be accurate.

chucktodd:
Doesn't adding digits past the decimal point show Increased resolution?

No. Just meaningless numbers.
With default Aref, you have 75mV/5mV = 15 steps spread over 50Amp.
With 1.1volt Aref enabled, you have ~75 steps.
If you increase the current, you will see 0.6666, 1.3333, 1.9999 etc. on the display.
Nothing in between.
Leo..

Wawa:
No. Just meaningless numbers.
With default Aref, you have 75mV/5mV = 15 steps spread over 50Amp.
With 1.1volt Aref enabled, you have ~75 steps.
If you increase the current, you will see 0.6666, 1.3333, 1.9999 etc. on the display.
Nothing in between.
Leo..

I guess I was too opaque. :o I expected the OP to actually do the division, and realize that a 75mV sensor directly connected to a 10bit 0..5V ADC would be almost useless.

The only way to use that sensor is with a higher resolution ADC, the ADS1118 is a 16bit SPI interface chip with a minimum FullScale range of +-256mV. So mapping his 75mV sensor over the 256mV 16bit range gives a digital range of 0..9600. Each bit is worth 0.005208 A.

Yes, by re-configuring the ADC to use it's 1.1v internal reference you would get better resolution, but, based on how he wrote his question. I think it would have been over his head to suggest it.

I apologize. I was being too snarky.

Chuck.

Hi,
Where abouts in the circuit have you placed the shunt, this is very important as the arduino measures between its gnd and analog input.

As has been pointed out earlier, you will not have much resolution in your readings, you may have to amplify the shunt output to get your voltage to a level more suited to the arduino 0 to 5V input.

Tom....

You really need some gain to get reasonable resolution.

An old NatSemi trick is something like the attached -it gives 1v/amp

regards

Allan.

note the opamp must work with inputs at around Vcc

HiI.pdf (18.4 KB)

Post#3. 0-100volt.
That excludes high-side current measurements.

The INA169 (<= 60volt) does the same as your diagram.

Leo..

Not necessarily - you' have to offset the Vss of the opamp from gnd, and have a level translator down to Q1. Very low currents are involved with suitable devices - <1mA.

I've done it.

regards

Allan.

Just found the INA193 (80volt).

Don't know what OP wants to measure (100volt/100Amp).
If accuracy is not a big issue, then some form of hall sensor might be easier.
Leo..

ok,

thanks to all of you, i will try...